This invention relates to a guide wire, especially a guide wire used to guide a catheter or other tubular medical devices to a target place in the body of a patient.
A guide wire is used to guide a catheter in treatment of the body parts on which open surgery is difficult or in treatment or examination for the purpose of reducing the invasiveness to the body such as PTCA (Percutaneous Transluminal Coronary Angioplasty) and cardiovascular angioplasty to the target place in the body. The guide wire used in the PTCA procedure is passed through the catheter before the catheter is inserted into a blood vessel, and the guide wire is used to guide the catheter to the vicinity of the target stenosed part in a blood vessel.
The guide wire used in the PTCA process is inserted in a blood vessel together with the catheter, with the distal end portion of the guide wire being protruded from the distal end of the catheter, to the vicinity of the target stenosed part in a blood vessel, and guides the distal end portion of the catheter to the target stenosed part. The distal end portion of the catheter has various shapes according to the purpose and the location in the body for which the catheter is designed, and has a flexibility which allows the catheter to follow complicated shapes of blood vessels and other organs in the body.
Since blood vessels bend in a complicated manner, a guide wire used to insert a catheter into a blood vessel must have a proper flexibility, pushability and torque-transmitting capability (operatability is a generic term for these two properties in combination), and kink resistance (property which resists sharp bending). A guide wire can have a metal coil with an appropriate flexibility attached around the distal end portion of a small-diameter core material to provide a proper amount of flexibility, or the guide wire can use a wire of a super elastic alloy such as Ni-Ti as the core material.
Conventional guide wires have a core material formed of substantially a single material, and a material with a relatively high rigidity is used to increase the operatability of the guide wire. As a result, the distal end portion of guide wire does not have a sufficient flexibility. On the other hand, if a material with a relatively low rigidity is used to increase the flexibility of the distal end portion of the guide wire, the operatability of the proximal end portion decreases. Therefore, it has been thought that is difficult to satisfy both the requested flexibility and operatability with a single core material.
To solve this problem, a guide wire is known which uses a core material formed of Ni-Ti alloy, for example, and having its distal end portion heat-treated and proximal end portion in different conditions to increase the flexibility of the distal end portion and the rigidity of the proximal end portion. However, there is a limitation of the control of flexibility by such heat treatment; it is not always possible to give the proximal end portion a satisfactory rigidity while making the distal end portion sufficiently flexible.
A guide wire made by joining a Ni-Ti alloy wire and a stainless steel wire with a tubular connector of Ni-Ti alloy to satisfy the desired flexibility for the distal end portion and a high rigidity for the proximal end portion is disclosed in Japanese Patent Application Laid Open No. 1992-9162. Since the tubular connector of Ni-Ti alloy used in this invention has a uniform rigidity over the entire length, there is a relatively large difference in the rigidity between the Ni-Ti alloy wire and the stainless steel wire which have different rigidities. As the result, a stress concentration occurs at the joint of the Ni-Ti alloy wire and the stainless steel wire, which can cause kink or decrease the operatability.